Keep in mind that the boosters flip around and initiate a burn to get back over land. As far as i'm aware, the core maintains a primarily ballistic trajectory and thus lands out in the ocean.
The boostback burn is a hell of a thing too, there was a Space Shuttle contingency plan called RTLS that was essentially the same thing. IIRC one of the commanders described it as "an unholy act of physics". This is quite similar, albeit with much less mass.
Yeah, the major complication with the STS RTLS option is that the Shuttle had to keep the external fuel tank until after the return burn was completed (since the shuttle itself carried no propellant for the main engines).
Scott Manley did a video a few years back explaining how this return profile works (and attempting to fly it in Orbiter)
Also (IIRC) you wanted the external tank to have as little remaining propellant in the main tank as possible, to facilitate separation without impacting the tank. Which meant that your burn times didn't really change when aborting, which is not a common feature of spacecraft abort systems to say the least.
And there was no way to eject the SRBs early, either. Once those lit, you were in for a ride...
The space shuttle had far more black zones in its launch profile than would have been acceptable in the Saturn program, or any manned program since.
Yeah, the tank had to be empty before it could be dropped (so the RTLS profile actually involved continuing away from the launch site for a while in order to burn off all the fuel without overshooting the return).
